Process for preparing polymeric vinyl esters in granular form



Patented Mar. 19, 1940 UNITED STATES.

PATENT OFFICE PROCESS FOR PREPARING POLYNIERIC VINYL ESTERS IN GRANULAR FORM No Drawing. Application May 5, 1938, Serial No. 206,276. In Great Britain October 25, 1933 15 Claims. (01. 260-37) This invention relates to the production of plastic materials by the polymerization of vinyl esters and, more particularly, to the polymerization of vinyl acetate in granular form. The

application is a continuation in part of our copending application 749,500, filed October 22, 1934.

It has already been proposed to polymerize vinyl esters and other polymerizable compounds by emulsifying such compounds in liquids in which they are substantially insoluble and subsequently polymerizing them. In such previous proposals, however, the unsaturated ester compounds were generally vfirst emulsified and then subjected to polymerizing conditions. Proceeding by these methods involves a number of steps: (1) the addition to the monomer containing a polymerization catalyst of the emulsifying agent and a nonsolvent for the monomer, (2) emulsifying the so resulting mixture, (3) polymerizing the emulsion, (4) adding coagulating agent, (5) coagulating the emulsified polymer, 6) removing the coagulating agent. The ultimate product obtained by such a procedure, furthermore, is not generally in a g; form which is easily dissolved, molded, or otherwise iabricated into an article of commerce.

We have now discovered that vinyl esters or mixtures of the same can be caused to yield polymerization products in granular or globular form,

providing the polymerization is effected in the presence of a suitable liquid medium and with proper agitation whereby agglomeration of the individual droplets, on the one hand, and their extended dispersion, on the other, are prevented.

Moreover, many of the disadvantages inherent in the emulsion polymerization process are eliminated by our process. It involves no emulsification prior to polymerization; no addition of coagulating agent for the product of our invention is free settling; no coagulation step, and hence no coagulating agent to remove; and most important the free settling product of our invention is in such form that it may be readily washed,

dissolved, molded or otherwise treated for use in the various arts for which it is adapted. Furthermore, as would be expected, because of its high state of subdivision, the polymer obtained by the emulsion process has a low bulk density which is not readily adapted to commercial molding and considerable difflculty is encountered in attempting to pellet or otherwise compress this product. In contradistinction the granular product of this application has a high bulk density 3 and is molded with facility.

Generally speaking, the production of the polymerization product in granular or globular form is effected by adding the monomeric unsaturated compound to a non-solvent liquid therefor containing a colloid, the resulting mixture is stirred, 5 its temperature raised, and the stirring, amount of colloid, and temperature maintained at the proper degree until polymerization is complete. When the stirring is stopped the polymerized resin settles freely and substantially instantaneously, "10

the supernatant liquid is decanted, and the product is washed and dried. The finished product consists of fine spherical granules, varying in size from to 5 mm. in diameter according to the conditions of polymerization, in contradistinction u to the slimy product resulting from the coagulation of the emulsion polymer. To obtain such a unique and surprisingly useful polymerization product by the process that will hereinafter be more fully particularized is, in view of the prior go art, most unexpected.

When polymerizing in accord with the general method 'hereinabove disclosed, it will be found that the form of the polymerized resin will vary in accord with degree of stirring, and concentra- 25 tion of colloid. The feature of the present invention is to so regulate these factors that a product in granular or globular form is. obtained which is readily removed from the polymerizing solution and may be easily filtered and washed. 3 It will be appreciated that, if the rate of stirring of a given system containing a monomer, a nonsolvent therefonand a colloid is sufliciently great, an emulsion will result, and it has been found that upon polymerization thereof there is obtained a 35 permanent suspension of minutely small particles. Such a product is then coagulated to a slime which is most diflicult to wash to remove coagulating agent. Alternatively, should the stirring of a given system be carried out at a very moderate 40 rate, very little, if any, emulsification or dispersion of the monomer will be effected and in many instances the monomer upon polymerizing will form a hard horny solid layer which sticks tenaciously to the vessel and stirrer and can be removed therefrom only with great difliculty.

In lieu of varying the rate of stirring the amount of colloid may, of course, be varied. Assuming now for the moment that an optimum stirring rate be employed, it is conceivable, and has been found by experiment to be actually a fact, that if a large amount of the colloid be employed, say, for example, 4% of glycol cellulose,

a product similar to that obtained by very vigorous stirring will result, i. e. an emulsion polymer,

while, on the other hand, should concentrations of this colloid be maintained at in the neighborhood of, say, 0.01%, a product comparable to that of mild stirring will be obtained.

We have found, however, that by following the directions hereinafter to be specified, it is possible to so control the above factors that the polymerized product will be in a granular 'or globular form, which is very easily filtered and washed from the dispersing medium. As has been indicated, the stirring should not be too violent nor the amount of colloid so great that after completing the polymerization a permanent emulsion of the polymer results.

Accordingly, in order to obtain the product of this invention we have found that stirring should be used in amount substantially equivalent to that obtained in an ovaled bottom enameled vessel containing no bailles having acapacity of 50 gallons and provided with a stirrer of a flat inverted r type x 1%") occupying 0.4 diameter of the pot and immersed 10 inches in the solution, the vessel having been charged with gallons of water containing 0.3% of glycol cellulose and 5 gallons of monomeric vinyl acetate containing 1% of benzoyl'peroxide, the stirrer being revolved at 510 R. P. M. The solution is heated to a temperature of 66 C. which is gradually increased to about 90 C. as the polymerization proceeds. It will be found that after a period of approximately 5 to 8 hours, under these conditions, the monomer will be substantially entirely converted to a polymer which is in granular form and which settles freely and quickly upon stopping the stirrer. If in this example the concentration of glycol cellulose be increased to 4%, an emulsion is obtained that gives a slimy product upon coagulation. On the other hand, should the amount of glycol cellulose be lowered to approximately 0.01% the polymerization will proceed with simultaneous fusion of the particles of polymer to each other, giving a solid, horny mass, which will adhere firmly to the vessel and often stop the stirring mechanism entirely, and necessitate destruction of the vessel in many instances before the resin can be removed therefrom.

An object of this invention, therefore, is to, on the one hand, conduct the polymerization of the herein named bodies under such conditions and concentrations that the emulsified product or alternatively the solid, horny mass is not obtained. Between these extremes, then, lies applicants process and they have found that by proper coordination of stirring and character and concentration colloid, it is possible to keep between the two undesirable limits and obtain the preferred product.

According to the present invention, plastic materials may be obtained in granular or globular form by polymerizing, in the manner hereinbefore indicated, vinyl'esters of organic or inorganic acids or mixtures of the same, and more particularly vinyl acetate, vinyl formate, vinyl propionate, vinyl chloride, vinyl bromide and the like. Mixtures and interpolymers of these various compounds with each other or with other polymerizable compounds such as the halogenated vinyl esters, etc., may likewise be polymerized by the process of the present invention.

As has been indicated, the proportions of the colloids will vary in large measure in accord with their ability to act as a dispersing agent, but generally speaking lyophilic colloids are preferred. By the term lyophilic colloid as employed herein, we mean to include a high molecular weight material which has an afllnity for the dispersing medium. Compounds such as soluble starch, gum tragacanth, gum acacia, gum tragon, water soluble glycol cellulose, sodium alginate, agar agar, glue and gelatin may be used. Glycol celluloses which are soluble in sodium hydroxide, altho insoluble in water, may

'be used in very dilute alkaline solutions. Ordinarily, these colloids and colloids having like dispersing powers may be used in concentrations varying from .2 to 3%, altho in some instances more may be required. the percentage being based upon the weight of the unsaturated compound being polymerized. Those skilled in the art will appreciate the fact that the enumerated colloids all do not have equal dispersing powers, e. g., gum tragacanth is less effective than glycol cellulose and various types of starches vary in accord with the past history of the starch. Ac-

cordingly, when changing from one colloid to the reaction mixture may be prepared by adding the aqueous or other type of solution to the un-' saturated compound or vice versa. The former method is preferred.

By what has been said it will be appreciated that agitation is essential from the inception of the actual polymerization until the product is substantially completely polymerized, since the medium in which the unsaturated compound is treated is of such a type that separation in two liquid phases takes place if the agitation is interrupted before or shortly after the inception of polymerization.

The process of this invention results in the production of the polymerized material in the form of solid granules or globules which are chemically and physically homogeneous, altho the particles may or may not be of such small diameter that the material has a powder-like appearance in bulk. This product, as has here- I inbefore been emphasized, is particularly easy to remove from the polymerization vessel and may be applied directly for any purpose for which the polymer is commonly employed without the necessity of previous grinding, cutting, or other comminuting treatment.

The polymerization may be effected, for instance, by heating the mixture in contact with a polymerization catalyst, or by subjecting it to ultraviolet light, agitation being continued un-. til the polymer is no longer sticky. The polymer will thus be produced. Similarly, dyed, tinted, or filled polymer may be obtained.

As the heat evolved in the polymerization of these compounds is frequently large, a part only of the charge of the monomeric compound may be mixed with the aqueous or other medium at the commencement of polymerization, the remainder of the monomer being added gradually thereafter so as to maintain the evolution at a given rate. a

The invention is illustrated by the following example in which all parts are by weight:

' Example 5 parts of benzoyl peroxide were dissolved in 500 parts of vinyl acetate, and the solution stirred with 1,000 parts of 0.5% gylcol cellulose solution, with warming. Polymerization occurred with vigorous evolution oi heat. Monomeric vinyl acetate and water which boiled oil from the reaction mixture were condensed and returned to the system. On completion of polymerization, the mixture was cooled down, and the granular polymerized vinyl acetate drained from the aqueous portion, washed with cold dilute caustic soda, then with cold water, and spread out in thin layers on trays to dry at atmospheric temperature.

From a consideration of the above specification it will be appreciated that many changes may be made in the invention as covered in the appended claims without departing from its scope.

We claim:

1. A process for the preparation of vinyl ester polymers in granular form which comprises dispersing and polymerizing while thus dispersed a monomeric vinyl ester in a non-solvent there- .for, by means of a dispersing agent and stirring,

the concentration of the dispersing agent being not substantially greater than an amount sufficient, to maintain the ester in the dispersed phase while stirring is continued, and, to prevent coalescence of the dispersed particles during polymerization, the quantity of dispersing agent also being insuflicient to give a permanently dispersed product.

2. A process for the preparation of vinyl esters in granular form which comprises dispersing and polymerizing while thus dispersed a monomeric vinyl ester in water by means of a dispersing agent and stirring, the concentration of the dispersing agent being not substantially greater than an amount suflicient, to maintain the esters in the dispersed phase while stirring is continued, and, to prevent coalescence of the dispersed particles during polymerization, the quantity'of dispersingagent also being insumcient to give a permanently dispersed product.

3. A process for the preparation of vinyl acetate polymer in granular form which comprises dispersing and polymerizing while thus dispersed monomeric vinyl acetate in a non-solvent therefor, by means of a dispersing agent and stirring,

the concentration of the dispersing agent being not substantially greater than an amount sufficient to maintain the ester in the dispersed phase while stirring is continued, and, to prevent coalescence of the dispersed particles during polymerization, the quantity of dispersing agent also being insuflicient to give a permanently dispersed product.

4. A process for the preparation of vinyl acetate polymer in granular form which comprises dispersing and polymerizing the thus dispersed monomeric vinyl acetate in water by means of glycol cellulose, the contration of glycol'cellulose being not substantially greater than that necessary to maintain the monomeric ester in the dispersed phase while stirring is continued, and, to prevent coalescence of the dispersed particles of the vinyl acetate during its polymerization. the quantity of dispersing agent also being insuiiicient to give a. permanently dispersed product.

5. A process for the preparation of vinyl ester polymers in granular form which comprises dispersing and polymerizing while thus dispersed a monomeric vinyl ester in a non-solvent therefor, by means ofa colloid selected from the group consisting of asoluble starch, gum tragacanth, gum acacia, gum tragon, water soluble glycol cel lulose, sodium alginate, agar agar, glue and gelatin and stirring, the concentration of the colloid being not substantially greater than an amount suillcient to maintain the ester in the dispersed phase while stirring is continued, and, to prevent coalescence of the dispersed particles during polymerization, the quantity of dispersing agent also being insuflicient to give a permanently dispersed product.

6. In a process for the preparation of vinyl ester polymers in granular form the step which comprises maintaining a dispersion of the monomeric vinyl ester by means of a colloid selected from th group consisting of a soluble starch, gum tragacanth, gum acacia, gum tragon. water soluble glycol cellulose, sodium alginate, agar agar, glue and gelatin and stirring thruout polymerization, the concentration of colloid and the rate of stirring being such that upon cessation of stirring before polymerization has been effected substantially all of the monomeric vinyl ester will quickly coalesce to the liquid phase and upon cessation of stirring after polymerization the vinyl ester polymer will freely settle as a granular product.

'7. In a process for the preparation of vinyl acetate polymer in granular form the step which comprises maintaining the vinyl acetate monomer in the dispersed phase by means of a colloid selected from the group consisting of a soluble starch, gum tragacanth, gum acacia, gum tragon, water soluble glycol cellulose, sodium alginate, agar agar, glue and gelatin and stirring -thruout the polymerization reaction, the concentration of the colloid and the rate of stirring being such that upon cessation of stirring before polymerization has been effected substantially all of the vinyl acetate monomer will quickly coalesce to the liquid phase, and upon cessation of stirring after polymerization the vinyl acetate polymer will freely settle as a granular product.

8. In a process for the preparation of vinyl acetate polymers in granular form the steps which comprise polymerizing in a liquid mixture containing vinyl acetate and a non-solvent therefor, in the presence of a sufllcient quantity of a colloid selected from the group consisting of a soluble starch, gum tragacanth, gum acacia, gum tragon, water soluble glycol cellulose, sodium alginate, agar agar, glue and gelatin while maintaining a proportional amount of stirring to give a product the particles of which will not coalesce to produce a solid during polymeriza tion, the amount of colloid and the amount of stirring being insufllcient to give a permanently emulsified product.

9. In a process for the preparation of vinyl acetate polymers in granulariorm the steps which comprise polymerizing in an aqueous medium containing monomeric vinyl acetate, in the presence of a suflicient quantity of colloid selected from the group consisting of a soluble starch, gum tragacanth, gum acacia, gum tragon,

5 'water soluble glycol cellulose, sodium alginate,

agar agar, glue and gelatin while maintaining a moderate amount of stirring to give a product the particles ofwhich do not coalesce to produce a solid during polymerization, the amount of colloid and the amount of stirring being insuflicient to give a permanently emulsified product.

10. In a process for the preparation of vinyl acetate polymers in granular form the step which comprises polymerizing the vinylacetate in a mixture containing approximately one part of, vinyl acetate to four parts of water, and approximately 0.2% to 3.0% of a colloid selected from the group consisting of a soluble starch, gum tragacanth, gum acacia, gum tragon, water soluble glycol cellulose, sodium alginate, agar agar, glue and gelatin while maintaining a proportional amount of stirring which is suflicient to give a product the particles of which do not coalesce to produce a solid during polymerization,- altho not so great that a permanently emulsified product is obtained upon complete polymerization.

11. In a process for the preparation of vinyl ester polymers in granular form the step which comprises polymerizing, in a liquid mixture containing the vinyl ester and a non-solvent there-v for, and in the presence of a suflicient quantity of a colloid selected from the group consisting of a soluble starch, gum tragacanth, gum acacia, gum tragon,water soluble glycol cellulose, sodium alginate, agar agar, glue and gelatin while maintaining a proportional amount of stirring to give a free settling product of separate and distinct particles ranging from A, .to 5 mm. in diameter.

12. A process for the preparation of vinyl ester polymers in granular form which comprises preparing a liquid mixture containing a monomeric vinyl ester, a non-solvent therefor,

and a colloid selected from the group consisting" of a soluble starch, gum tragacanth, gum acacia,

gum tragon, water soluble glycol cellulose, sodium alginate, agar agar, glue and gelatin, stirring the resulting mixture to give a dispersion such that upon cessation of stirring the particles the monomer will substantially immediately coalesce,

heating the dispersed mixture until polymerization is complete, and subsequently stopping the stirring and separating by decantation the free settling granular vinyl ester polymer irom the dispersing medium.

l3. Aprocess for the preparation of vinyl acetate polymers in'granular form which comprises preparing a liquid mixture containing monomeric vinyl' acetate, a non-solvent therefor,

and a colloid selected from the group consisting a of a soluble starch, gum tragacanth, gum acacia,

gum tragon, water soluble glycol-cellulose, sodium alginate, agar agar, glue'and gelatin, stirring the resulting mixture to give a dispersion such that upon cessation of stirring the particles of monomer will substantially immediately coalesce, heating the dispersed mixture until polymerize. tion is complete, and subsequently stopping the stirring and separating by decantation the free settling granular vinyl acetate polymer from the dispersing medium.

14. A process for the preparation of vinyl esters in granular form which comprises dispersing a monomeric vinyl ester in water by means of v a dispersing agent present in an amount not substantially greater than the amount necessary to maintain the ester in the dispersed phase while stirring is continued and to prevent coalescence of the dispersing particles during polymerization, the quantity of dispersing agent also being insumcient. to give a permanentlydispersed product,- the polymerization being initiated by raising the itemperature to approximately 66 C. and

proximately 66 C, and during polymerization being maintained at a temperature between approximately 66 C. and C.

JOHN WILLIAM CROOM CRAWFORD. JAMES MCGRA'I'H.

maintaining the temperature during polymerization ,loetween approximately 66 C. and 90 C. 

